1. Field of the Invention
The present invention relates to a semiconductor memory device. More particularly, it relates to a semiconductor memory device having a high-speed serial data input and output circuit in addition to a random data input and output circuit.
2. Description of the Related Art
An image data processing system or the like requires a large-capacity memory. To meet the requirement for a large-capacity memory at low cost, a dynamic random-access memory (RAM) is extensively used. In addition, in order to display a large amount of image data stored in the RAM on a cathode ray tube (CRT) display unit and perform image data processing for the large amount of image data, such as gradients and filtering, high-speed data store and/or read-out are also highly required. A normal semiconductor memory device having a dynamic RAM and operable for random access for each unit of data, per se, however, suffers from a disadvantage of low-speed data store and/or read-out for a large amount of image data.
Recently, in order to overcome the above disadvantage, there are known so-called dual-port memory devices, i.e., semiconductor memory devices including a high-speed data input and output circuit provided outside the dynamic RAM. A dual-port memory device is operable for not only normal random access through a conventional port, but also high-speed serial data input and output used by a high-speed data input and output circuit through another port.
These prior art semiconductor memory devices, however, still suffer from disadvantages of complex circuit configurations, use of a considerably large space on the semiconductor chip, which may lead to low integration, and high power consumption.